This invention relates in general to voltage controlled oscillators and in particular, to high frequency voltage controlled oscillators including a plurality of voltage controlled differential inverting delay cells forming a ring oscillator.
Applic. Ser. No. 08/169,150 of Zhongxuan Zhang, entitled "Improved Differential Amplifier and Variable Delay Stage for Use in a Voltage Controlled Oscillator," and which is incorporated herein by this reference, describes a differential amplifier useful as a delay cell in a ring oscillator of a voltage controlled oscillator. The differential amplifier includes a pair of clipper transistors coupled as a pair of diodes across its output nodes for limiting the voltage swing at its output nodes to a threshold voltage of the clipper transistors. By limiting the voltage swing at its output nodes, rather than allowing it to swing rail to rail as in prior art differential amplifiers, the frequency response of the differential amplifier is improved over such prior art differential amplifiers.
Applic. Ser. No. 08/455,311 of Zhongxuan Zhang and He Du, entitled "Voltage Controlled Oscillator including Voltage Controlled Delay Circuit with Power Supply Noise Isolation," and which is incorporated herein by this reference, describes a voltage controlled oscillator including a plurality of voltage controlled differential inverting delay cells, wherein a control voltage is provided to each of the voltage controlled differential inverting delay cells through a source-follower transistor having a drain electrode connected to a power supply, a gate electrode connected to the control voltage, and a source electrode connected to the voltage controlled differential inverting delay cell such that the source-follower transistor provides the control voltage to the voltage controlled differential inverting delay cell while effectively isolating the voltage controlled differential inverting delay cell from noise on the power supply line.
In certain applications such as in high speed peripheral controllers for computer systems, it is desirable to further enhance the performance and in particular, the frequency response of a voltage controlled oscillator used therein.